Ice Jams on Area Streams - updated 1/13/2010

Ice jams continue on portions of the Fox, Rock, and Kankakee Rivers. Warming daytime high temperatures this week may result in some melt and ice movement within the rivers. However, it does appear as though ideal melt conditions will prevail with temperatures rising above freezing during the day and falling back below freezing during the night. This will help to regulate the expected melt and runoff from snowmelt.

When an ice jam forms, water levels can rise quickly with little or no warning. Residents living in low lying areas along rivers prone to ice jams should continue to closely monitor water levels and be prepared to move quickly if ice jam flooding occurs.

The following images provide a dramatic comparison of normal river stages to levels experienced on Jan 5, 2010 due to a significant ice jam on the Fox River at Dayton, IL.

Lower Fox River at Dayton, IL

Jan 5, 2010
looking upstream

Aug 2009
looking upstream

Jan 5, 2010
looking downstream

Aug 2009
looking downstream

Rock River at Dixon, IL

Rock River at Dixon, IL Jan 3, 2010
Photo by Rick Bernotas

Rock River at Dixon, IL Jan 3, 2010
Photo by Rick Bernotas

Ice Breakup

Once an ice cover exists on the river, what causes it to melt or break? An ice cover can breakup thermally or "mechanically".

A thermal breakup simply means that warm temperatures and direct sunlight allow the ice cover to melt in place. This is the ideal situation. Typically a thermal breakup does not result in flash flooding.

A mechanical breakup occurs when forces act on the ice cover to break it apart. Heavy rainfall or a combination of rainfall and snowmelt creates runoff which increases flows below the ice cover. This increased flow helps to lift and break the ice. Rapid increases in flow can begin to break apart and move ice downstream in a short amount of time. Once the ice encounters an obstacle, it can quickly jam and result in flash flooding.

What Causes Ice Jams?

Ice jams form when ice flowing in the river channel encounters some obstruction that prevents it from moving downstream. Ice jams typically occur at:

Stream constrictions such as bridges

Sharp meanders in the stream

Obstructions such as islands

locations where there is a change in the slope of the streambed

When conditions are ideal for significant ice formation, ice jams tend to develop in the same areas.

Turn Around, Don't DrownTM

Each year, more deaths occur due to flooding than from any other severe weather related hazard. The Centers for Disease Control report that over half of all flood-related drownings occur when a vehicle is driven into hazardous flood water. The next highest percentage of flood-related deaths is due to walking into or near flood waters. Why? The main reason is people underestimate the force and power of water. Many of the deaths occur in automobiles as they are swept downstream. Of these drownings, many are preventable, but too many people continue to drive around the barriers that warn you the road is flooded.

Play it smart, play it safe. Whether driving or walking, any time you come to a flooded road, TURN AROUND, DON'T DROWN!